bug#43837: 28.0.50; [NS] Internal border of inactive frame loses color

[Eli Zaretskii]

> From: Andrii Kolomoiets <andreyk.mad@gmail.com>
> Date: Tue, 06 Oct 2020 22:40:33 +0300
> 
> In 'emacs -Q':
> 
> 1. M-: (setq test-frame (make-frame '((left . 50) (top . 50))))
> 2. C-x 5 o
> 3. M-: (set-face-background 'internal-border "blue" test-frame)
> 4. M-: (modify-frame-parameters test-frame '((background-color . "black")))
> 
> Now (face-background 'internal-border test-frame) returns nil.
> If we skip step 2, then the internal border color remains.

I think I fixed this on the master branch now.

Thanks.